JP2019003871A - Active material liquid and method of manufacturing active material liquid - Google Patents

Abstract

To provide an active material liquid which, in a vanadium high concentration system, avoids reduction in charge and discharge efficiency caused in the high concentration system by capable of preventing precipitation of vanadium even during temperature drop and stably maintaining cell output with respect to temperature change and also to provide a method of manufacturing the active material liquid.SOLUTION: An active material liquid of the present invention has sulfuric acid acidity and is a negative active material liquid or a positive active material liquid of a vanadium redox secondary battery whose all vanadium concentration is equal to or more than 2.5 M. By addition of chloride, a chemical shift value of proton peak in the proton nuclear magnetic resonance spectrum is 1.2 to 5 times of the chemical shift value in a sulfuric acid aqueous solution of 0.1 M to 10 M.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an active material liquid and a method for producing the active material liquid. More specifically, the present invention relates to a vanadium having a concentration higher than about 2M, which is the upper limit of solubility of an aqueous battery active material solution of conventional 2-4M sulfuric acid vanadium sulfate. In high-concentration systems, active material liquids and active materials that can prevent the precipitation of vanadium even when the temperature drops, maintain stable battery output against temperature changes, and avoid the decrease in charge / discharge efficiency caused by the high-concentration system The present invention relates to a method for producing a liquid.

  Secondary batteries are attracting attention as an energy storage source with a low environmental load that can repeatedly discharge and charge electricity. As secondary batteries for industrial use, lead storage batteries, sodium sulfur storage batteries, redox flow batteries and the like are known.

  In particular, a vanadium redox flow battery using a vanadium electrolyte operates at room temperature and can be stored in an external tank because the active material is liquid. Therefore, it is easy to increase the capacity (time ratio) by storing only the active material liquid, and unlike other secondary batteries, lithium ion batteries, nickel metal hydride batteries, etc., the active material is liquid, There are advantages such as easy reproduction and long life.

  Vanadium pentavalent and tetravalent redox pairs are used for the positive electrode active material liquid of the vanadium redox flow battery, and vanadium divalent and trivalent redox pairs are used for the negative electrode active material liquid (Patent Document 1). 2). In such a system, electrode reactions during charging and discharging are expressed as follows.

(Electrode reaction during charging)
Positive reaction: ^{VO 2+} _{(4-valent) + H 2 O → VO 2} + (5 valence) + ^2H + + e ^-
Negative electrode reaction: V ³⁺ (trivalent) + e ⁻ → V ²⁺ (bivalent)

(Electrode reaction during discharge)
Positive reaction: _VO ² + (5 ^{valence) + 2H + + e - →} VO 2+ (4 -valent) _{+ H} 2 O
Negative electrode reaction: V ²⁺ (divalent) → V ³⁺ (trivalent) + e ⁻

  In such a redox flow battery, the input / output density (or simply output density) and the storable power (or simply energy density) increase as the vanadium concentration in the liquid increases.

  In order to improve the power density (W / kg) and increase the energy density (Wh / kg), both the positive electrode active material and the negative electrode active material are increased in vanadium concentration, and the specific resistance and viscosity of the liquid are increased. It is important not to increase it, and such attempts have been made (Non-Patent Documents 1 to 3).

JP 62-186473 A Japanese Patent Laid-Open No. 4-28671

L. D. Kurbatova, D. I. Kurbatov, "Vanadium (V) extraction from sulfuric acid solutions", Russian Journal of Inorganic Chemistry, July 2008, 53 (7), 1154-1157 Faizur Rahman, Maria Skyllas-Kazacos, "Vanadium redox battery: Positive half-cell electrolyte studies", Journal of Power Sources, April 2009, 189 (2), 1212-1219 Ogaku et al., "V (II) / V (III) reaction in the negative electrode of vanadium redox flow battery", Proceedings of Battery Conference, November 04, 2003, 44, 630-631 M. Vijayakumar, Wei Wang, Zimin Nie, Vincent Sprenkle, JianZhi Hu, "Elucidating the higher stability of vanadium (V) cations in mixed acid based redox flow battery electrolytes", Journal of Power Sources, November 2013, 241 (1), 173-177

  Non-Patent Documents 1 and 2 report a sulfuric acid pentavalent vanadium-containing liquid that can be used as a battery positive electrode active material liquid.

  Non-Patent Document 1 clarifies that precipitation (crystallization) due to crystal growth of a vanadium salt is likely to occur when the vanadium concentration exceeds 2.0 M in a sulfuric acid pentavalent vanadium-containing liquid.

Moreover, it is said that it can be dissolved temporarily by adding sulfuric acid to the pentavalent vanadium-containing liquid in which such precipitation has occurred and heating it. However, the active material liquid obtained in this way is precipitated again when it is cold. In particular, pentavalent vanadium in the active material solution on the positive electrode side is easily precipitated as V ₂ O _{5 in} terms of equilibrium, and is quickly transferred to an equilibrium system in which precipitation occurs by heating, so that there is a problem of so-called thermal precipitation. _Therefore, the upper limit of the vanadium concentration in the system of only H 2 SO ₄ is _1.7～1.8M, the upper limit of the vanadium concentration in H 2 SO ₄ and HCl coexistence of mixed acid systems were set to about 2M. Therefore, in the extension of the current technology, it is important to maintain the precipitates as fine particles and use them as a high concentration active material. Since the deviation of the peak positions of the V ^{II / III} , V ^{IV / V} oxidation wave and reduction wave in the current-potential curve (cyclic voltamgram) of such a liquid is generally remarkably large, it is reversible. It can be seen that the reaction is poor. This result shows that it is difficult to use as a battery active material liquid having a large charge transfer resistance. Non-Patent Document 1 concludes that such an active material liquid has no practicality because of poor electrode response.

  Non-Patent Document 2 also reports the same knowledge as Non-Patent Document 1 based on the cyclic voltammogram.

  As described above, in the conventional positive electrode active material liquid composed of the sulfuric acid vanadium compound liquid, it is difficult to maintain sufficient solubility and fluidity under a free charge / discharge operation, particularly when vanadium is at a high concentration. In addition, it was difficult to perform stable and energy efficient charging / discharging.

  On the other hand, Non-Patent Document 3 reports a divalent and trivalent vanadium-containing liquid that can be used as a battery negative electrode active material liquid.

Non-Patent Document 3 performs chronopotentiometry in order to specify what kind of chemical species vanadium is present in the battery negative electrode active material solution. Thereby, the diffusion coefficient is obtained for each of divalent and trivalent vanadium in the liquid, and the Stokes radius of the chemical species is calculated from the actually measured viscosity. The calculated Stokes radius is an ako complex, specifically V ²⁺ (H ₂ O) ₆ or V ³⁺ (H ₂ O) ₆ , which has been conventionally considered as a chemical species of divalent and trivalent vanadium. It is confirmed that it is almost the same as the Stokes radius.

  Non-Patent Document 3 prepares a 1.6 M solution as a “practical vanadium concentration”. Also in the test results by the present inventor, it has been confirmed that in the conventional battery negative electrode active material liquid, the concentration capable of preventing the deposition of vanadium and continuing the charge / discharge stably is about 1.5M to 1.7M. Therefore, the concentration described in Non-Patent Document 3 can be said to be a reasonable value from the conventional viewpoint.

  As described above, the conventional negative electrode active material liquid composed of a sulfuric acid vanadium compound liquid is also difficult to maintain sufficient solubility and fluidity under free charge / discharge operation, particularly when vanadium is at a high concentration. Therefore, it was difficult to perform stable and energy efficient charge / discharge.

  The conventional attempts to increase the vanadium concentration have been described above with reference to Non-Patent Documents 1 to 3. Many patent documents describe vanadium concentrations exceeding 2M, but as described above with reference to non-patent documents, it is difficult to prevent the precipitation of vanadium in such a high concentration system. Yes, poor solubility and fluidity. This can be confirmed by actually conducting a test.

  Thus, in the prior art, in order to prevent the precipitation of vanadium salt in the active material solution, it was actually necessary to set the total vanadium concentration to a low concentration of about 1.5M to 1.7M. Therefore, there is a limit in realizing improvement in current density and increase in the amount of electricity that can be stored.

  It has been found that in the vanadium high concentration system in which the total vanadium concentration is 2.5 M or more, vanadium is likely to precipitate, and the precipitation becomes remarkable particularly when the temperature is lowered. In such a high concentration system, if the precipitation of vanadium can be prevented even when the temperature is lowered, the battery output can be stably maintained against the temperature change.

Note that Non-Patent Document 4 analyzes the stability of pentavalent vanadium in a mixed acid system by nuclear magnetic resonance spectrum measurement based on ⁵¹ V and ³⁵ Cl. However, now, ³⁵ Cl that may have partially coordinated to V ^- is the degree to which resonance absorption peaks of the observed effect of coexisting charge and discharge efficiency (for example, a voltage efficiency and the area resistivity) It was difficult to explain the chloride ion having a concentration of 1M that appears remarkably in the complex by only complexing to V.

  Therefore, the object of the present invention is to prevent the precipitation of vanadium even when the temperature is lowered in a high concentration system of vanadium, maintain the battery output stably against a temperature change, and reduce the charge / discharge efficiency caused by the high concentration system. An object is to provide an active material liquid to be avoided and a method for producing the active material liquid.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

(Claim 1)
A negative electrode active material liquid or a positive electrode active material liquid of a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more,
By adding chloride, the chemical shift value of the proton peak in the proton nuclear magnetic resonance spectrum is 1.2 to 5 times the chemical shift value in a 0.1 M to 10 M sulfuric acid aqueous solution. Active material liquid.
(Claim 2)
A positive electrode active material solution for a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more,
The chemical shift value of the proton peak in the proton nuclear magnetic resonance spectrum is 1.2 to 5 times the chemical shift value in a 0.1 M to 10 M sulfuric acid aqueous solution,
An active material liquid, wherein 0.2 M or more of chloride ions coexist with vanadium.
(Claim 3)
A negative electrode active material solution for a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more,
By adding chloride, the reaction electricity quantity of the oxidation wave of divalent vanadium in the current-potential curve observed by the potential sweep method is the reaction quantity Q ₀ measured at 0 ° C., and at 25 ° C. An active material liquid, wherein a ratio (Q ₀ / Q ₂₅ ) of measured reaction electricity Q ₂₅ is 0.3 to 1.0.
(Claim 4)
A positive electrode active material solution for a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more,
By adding chloride, the reaction electric quantity Q ₀ measured at 0 ° C. as the reaction electric quantity of the pentavalent vanadium reduction wave in the current-potential curve observed by the potential sweep method, and at 25 ° C. An active material liquid, wherein a ratio (Q ₀ / Q ₂₅ ) of measured reaction electricity Q ₂₅ is 0.3 to 1.0.
(Claim 5)
Viscosity is 6 cp or less, The active material liquid in any one of Claims 1-4 characterized by the above-mentioned.
(Claim 6)
When manufacturing a negative electrode active material liquid or a positive electrode active material liquid of a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more,
After electrolytic reduction of the vanadyl sulfate solution to make the molar ratio of trivalent vanadium and tetravalent vanadium 1: 1,
The chemical shift value of the proton peak in the proton nuclear magnetic resonance spectrum measured for the liquid in at least one of the following states (I) to (III) is 1.2, which is the chemical shift value in a 0.1 M to 10 M sulfuric acid aqueous solution. A method for producing an active material solution, wherein the sulfuric acid concentration and the chloride concentration are adjusted so as to be 5 times.
(I) Liquid in which the molar ratio of trivalent vanadium and tetravalent vanadium is 1: 1 (II) Liquid containing divalent vanadium and trivalent vanadium obtained by electrolytic reduction of the liquid described in (I) A liquid containing tetravalent vanadium and pentavalent vanadium obtained by electrolytic oxidation of the liquid described in (I).

  According to the present invention, in a vanadium high-concentration system, it is possible to prevent the deposition of vanadium even when the temperature is lowered, to stably maintain battery output against temperature changes, and to avoid a decrease in charge / discharge efficiency caused by the high-concentration system. An active material liquid to be produced and a method for producing the active material liquid can be provided.

^The figure which shows an example of < ¹ > H-NMR spectrum Cyclic voltammograms of negative electrode active material liquids according to Example 1 and Comparative Example 1 Cyclic voltammograms of positive electrode active material liquids according to Example 2 and Comparative Example 2 Temperature dependence of cyclic voltammogram of active material liquid according to Example (low temperature characteristics) Temperature dependence of cyclic voltammogram of active material liquid according to comparative example (low temperature characteristics)

  Below, the form for implementing this invention is demonstrated.

(First aspect of active material liquid)
The active material liquid according to the first aspect of the present invention is a negative electrode active material liquid or a positive electrode active material liquid of a vanadium redox secondary battery that is sulfuric acid acid and has a total vanadium concentration of 2.5 M or more.

The acidity of sulfuric acid means that it is acidic by adding sulfuric acid (H ₂ SO ₄ ). The degree of acidity is not particularly limited and is preferably pH 6 or less.

  The negative electrode active material liquid is an active material liquid containing divalent vanadium and trivalent vanadium, and the positive electrode active material liquid is an active material liquid containing tetravalent vanadium and pentavalent vanadium. In this specification, the negative electrode active material liquid and the positive electrode active material liquid may be referred to as a battery negative electrode active material liquid and a battery positive electrode active material liquid. Alternatively, the active material liquid may be simply referred to as the active material liquid including the bipolar active material liquid.

Such an active material liquid has a chemical shift value of a proton peak in a proton nuclear magnetic resonance spectrum (hereinafter also referred to as ¹ H-NMR spectrum) in a sulfuric acid aqueous solution of 0.1M to 10M by adding chloride. One characteristic is that it is 1.2 to 5 times the chemical shift value.

  According to the active material liquid according to the first aspect of the present invention, it is possible to prevent the deposition of vanadium even when the temperature is lowered, and the effect of stably maintaining the battery output against the temperature change is obtained.

^{In 1} H-NMR spectrum measurement, the chemical shift value δ _a of the resonance absorption peak of the battery negative electrode active material solution is measured at a predetermined resonance frequency using tetramethylsilane (TMS) as a reference material. On the other hand, similarly, tetramethylsilane (TMS) is used as the reference substance, and the chemical shift value δ _b of the resonance absorption peak of the sulfuric acid aqueous solution is measured at a predetermined resonance frequency. At this time, these chemical shift values satisfy δ _a ≧ 1.5 × δ _b . Since the ratio of these chemical shift values does not depend on the resonance frequency, the above-described predetermined resonance frequency used for the ¹ H-NMR spectrum measurement can be set as appropriate, but is preferably 200 kHz, for example.

An example of ¹ H-NMR spectrum will be described with reference to FIG.

  In FIG. 1, (a) is a spectrum of an aqueous sulfuric acid solution (concentration 6M), (b) is a spectrum of a battery negative electrode active material liquid, and (c) is a spectrum of a battery positive electrode active material liquid.

In the illustrated example, the chemical shift value δ _a (18 ppm) of the resonance absorption peak of the battery negative electrode active material liquid shown in (b) is 1.5 times the chemical shift value δ _b (12 ppm) of the resonance absorption peak of the sulfuric acid aqueous solution. Therefore, the above-described chemical shift value condition (1.2 times or more) is satisfied.

In addition, the chemical shift value δ _a (21 ppm) of the resonance absorption peak of the battery positive electrode active material liquid shown in (c) also corresponds to 1.75 times the chemical shift value δ _b (12 ppm) of the resonance absorption peak of the sulfuric acid aqueous solution. Therefore, the above-described chemical shift value condition (1.2 times or more) is satisfied.

When the condition of the chemical shift value in the ¹ H-NMR spectrum described above is satisfied, an active material liquid having preferable properties is obtained regardless of the presence or absence of Cl ⁻ . Cl ⁻ mainly interacts with HSO ₄ ⁻ and can greatly change the properties of the sulfuric acid-hydrochloric acid mixed water as a solvent.

(Second aspect of active material liquid)
The active material liquid according to the second aspect of the present invention is a positive electrode active material liquid of a vanadium redox secondary battery that is sulfuric acid acid and has a total vanadium concentration of 2.5 M or more, and has a proton peak in a proton nuclear magnetic resonance spectrum. Positive electrode activity of a vanadium redox secondary battery having a chemical shift value of 1.2 to 5 times the chemical shift value in a 0.1 M to 10 M sulfuric acid aqueous solution and a chloride ion of 0.2 M or more coexisting with vanadium. It is a substance liquid. A chloride ion can be 0.2-4M, for example, and it is preferable that it is 1M or more.

  According to the active material liquid according to the second aspect of the present invention, like the active material liquid according to the first aspect, it is possible to prevent the deposition of vanadium even when the temperature is lowered, and the battery is stable against temperature changes. The effect that the output can be maintained is obtained.

Normally, a ⁵¹ V nuclear magnetic resonance signal is not observed in a high concentration active material solution having a total vanadium concentration of 2.5 M or more. The reason for this is considered as follows.

That is, in a normal vanadium high-concentration active material solution, it is H ₂ O that is coordinated to V, and hydrogen sulfate ions (HSO ₄ ⁻ ) are likely to be present in the outer sphere. H 2 _O is d ² orbitals (internal orbital, the ligand exchange reaction rate of V ^III is generally greater) is weakly coordinated to, for the high spin, weaken the action and quadrupolar interactions paramagnetic I can't. Therefore, the ⁵¹ V nuclear magnetic resonance signal is extremely broad or buried in the background. In particular, since ⁵¹ V has a nuclear spin of 7/2, it is difficult to produce a nuclear magnetic resonance signal when it is dispersed by particles due to nuclear quadrupole interaction.

In contrast, in the active material solution according to the second aspect of the present invention, the suspendability is weakened by the coexistence of chloride ions as a ligand coordinated to the inner sphere of V contained in the positive electrode active material solution. In such a case, the ³⁵ Cl ⁻ signal is partially observed. However, since the effect of stabilizing this complex is limited, the effect of changing the properties of the solvent due to the coexistence of 0.2 M or more of Cl ⁻ is important from the viewpoint of exerting further effects. Thereby, like the active material liquid which concerns on a 1st aspect, precipitation of vanadium can be prevented also at the time of temperature fall, and the effect which can maintain a battery output stably with respect to a temperature change is acquired.

(Third embodiment of active material liquid)
The active material liquid according to the third aspect of the present invention is a negative electrode active material liquid for a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more.

Such an active material solution has a reaction electricity quantity Q measured at 0 ° C. as the reaction electricity quantity of the oxidation wave of divalent vanadium in the current-potential curve observed by the potential sweep method due to the addition of chloride. _0, the ratio of the reaction the quantity of electricity _{Q 25} measured at _{25 ℃ (Q 0 / Q 25} ), and one of the features that it is 0.3 to 1.0.

  By reforming the solvent (aqueous solution), it is possible to prevent the deposition of vanadium even when the temperature is lowered, and the effect of stably maintaining the battery output against the temperature change can be obtained. When the above conditions are satisfied, it means that the diffusion rate of vanadium in the liquid and the electron transfer rate on the electrode surface are not easily affected by the temperature drop. Furthermore, it is suggested that polymerization by vanadium oxidative crosslinking is also prevented, particularly when the temperature is lowered. Precipitation of vanadium can be largely suppressed by improving the fluidity of the liquid. Regardless of the addition of chloride, if the conditions of the chemical shift of the proton are satisfied, as in the above embodiments, by improving the properties of the solvent, it contributes to stabilization as an active material liquid Presumed.

(4th aspect of an active material liquid)
The active material liquid according to the fourth aspect of the present invention is a positive electrode active material liquid of a vanadium redox secondary battery that is sulfuric acid acid and has a total vanadium concentration of 2.5 M or more.

Such an active material solution has a reaction electricity quantity Q measured at 0 ° C. as a reaction electricity quantity of a pentavalent vanadium reduction wave in a current-potential curve observed by a potential sweep method due to the addition of chloride. _0, the ratio of the reaction the quantity of electricity _{Q 25} measured at _{25 ℃ (Q 0 / Q 25} ), and one of the features that it is 0.3 to 1.0.

  Thereby, the same effect as the 3rd mode is acquired.

  In the third and fourth embodiments of the active material liquid described above, cyclic voltammetry (hereinafter also referred to as CV measurement) can be preferably used as the potential sweep method. When measuring the amount of reaction electricity at 0 ° C. and 25 ° C., the same conditions except for the temperature are set. The amount of reaction electricity can be obtained as the area (peak area) of an oxidation wave or a reduction wave.

  The active material liquid according to the first to fourth aspects described above preferably has a viscosity of 6 cp or less. Thereby, the restraint property of the vanadium compound or ion which is an active material in the active material liquid is greatly relaxed, the diffusion rate is improved, and the current density at the time of battery charge / discharge is improved. In particular, when the active material liquid is circulated through a fibrous or particulate electrode such as conductive carbon fiber or conductive carbon fine particle or the like, if the fiber diameter or particle size is small (for example, several μmφ or less) ) The diffusion becomes multidimensional, and the effect of improving the current density becomes remarkable. Moreover, the effect of reducing the pressure loss at the time of distribute | circulating this active material to a battery cell is also acquired. Here, the viscosity of 6 cp or less is a value at room temperature (20 ° C.) using a viscometer of a type in which the liquid descends in the tube. Although the minimum of a viscosity is not specifically limited, For example, it can be 1 cp or more.

(Method for producing active material liquid)
The method for producing an active material liquid of the present invention is preferably used when producing a negative electrode active material liquid or a positive electrode active material liquid of a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more.

  In such a method for producing an active material solution, first, a vanadyl sulfate solution is electrolytically reduced so that the molar ratio of trivalent vanadium and tetravalent vanadium is 1: 1.

Then, the chemical shift value of the proton peak in the ¹ H-NMR spectrum measured for at least the liquid in any of the following states (I) to (III) is ¹ of the chemical shift value in the 0.1 M to 10 M sulfuric acid aqueous solution. One characteristic is that the sulfuric acid concentration and the chloride concentration are adjusted so as to be 2 to 5 times.
(I) Liquid in which the molar ratio of trivalent vanadium and tetravalent vanadium is 1: 1 (II) Liquid containing divalent vanadium and trivalent vanadium obtained by electrolytic reduction of the liquid described in (I) A liquid containing tetravalent vanadium and pentavalent vanadium obtained by electrolytic oxidation of the liquid described in (I).

  As the chloride, concentrated hydrochloric acid which is an aqueous solution of hydrogen chloride is preferable. If the concentration of free sulfuric acid in the solution to which hydrochloric acid is added is small, the vapor pressure of hydrogen chloride itself is small, and if the chemical shift value in proton NMR is actually in the above-mentioned region, the concentration of HCl does not matter. The concentration of HCl can be, for example, 0.2-4M, preferably 1-4M.

  According to the method for producing an active material liquid of the present invention, an active material liquid capable of preventing the deposition of vanadium even when left for a long period of time is obtained. By using the active material liquid, a high concentration of 2.5 M or more is obtained. However, the effect that the battery can be stably operated can be obtained.

  The liquid (I) is preferably used as a precursor before it becomes a liquid (ie, liquid (II) or liquid (III)) when the battery is actually charged and charged / discharged. it can. That is, after the liquid (I) prepared in advance is filled in each of the negative electrode chamber and the positive electrode chamber of the battery, the liquid (II) is electrolyzed in the negative electrode chamber as a result of electrolytic reduction by electrolyzing them. As a result of the oxidation, the liquid (III) can be generated in the positive electrode chamber.

Therefore, when the ¹ H-NMR spectrum in the liquid (I) satisfies the above conditions, the vanadium can be suitably prevented from precipitating when the liquid is distributed as a precursor on the market. The effect that can be improved is obtained.

Further, when the ¹ H-NMR spectrum in the liquid (II) or the liquid (III) satisfies the above conditions, vanadium is more reliably deposited when the battery is actually charged and charged / discharged. The effect that the battery output can be maintained more stably with respect to the temperature change is obtained.

  Further, in the method for producing an active material liquid of the present invention, as described above, the chloride ratio is added after the molar ratio of trivalent vanadium and tetravalent vanadium is 1: 1, thereby generating chlorine gas during electrolysis. The effect which can prevent suitably is acquired. In the present invention, the effect of suitably preventing the generation of chlorine-based gas is exhibited not only in the production process or storage process of the active material liquid, but also when the battery is actually charged and charged / discharged.

In the present invention, the chloride added to the active material liquid includes, for example, HCl, and can be added so that the chloride ion concentration in the active material liquid is 0.2 to 4M. The active material solution preferably has an apparent sulfate radical / chloride ion molar ratio of about SO ₄ ²⁻ : Cl ⁻ = 1: 1 to 3: 1.

  The chloride may be added in combination with other halides such as fluoride, bromide, iodide, etc., but is preferably added alone without being combined with other halides. Chloride has the advantage of strong interaction with sulfuric acid compared to other halides.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  In the following examples, “1. Battery negative electrode active material liquid” and “2. Battery positive electrode active material liquid” are verified, respectively, and then “3. Low temperature characteristics of active material liquid” are verified.

1. Battery negative electrode active material liquid (Example 1)
By electroreducing a solution containing 2.5 M VOSO ₄ and 2.0 M H ₂ SO ₄ in water, the molar ratio of trivalent vanadium and tetravalent vanadium was 1: 1 (3.5 valence). Furthermore, this solution was electrolytically reduced to obtain a solution containing divalent and trivalent vanadium. The viscosity of this liquid was 6 cp.

Next, when hydrochloric acid was added to the obtained liquid so as to satisfy the condition of the chemical shift value of the ¹ H-NMR spectrum described above, the hydrochloric acid concentration in the liquid became 0.4 M as a result. This was used as a battery negative electrode active material liquid. The viscosity of the solution after addition of hydrochloric acid was 4 cp.

^<1 H-NMR spectrum measurement>
The obtained battery negative electrode active material solution was subjected to ¹ H-NMR spectrum measured at a resonance frequency 200kHz, ¹ H-NMR spectrum shown in was obtained FIG 1 (b). The chemical shift value δ _a (18 ppm) of the resonance absorption peak of the battery negative electrode active material liquid corresponds to 1.5 times the chemical shift value δ _b (12 ppm) of the resonance absorption peak of the sulfuric acid aqueous solution. The condition (1.2 times or more) is satisfied.

<CV measurement>
When the obtained battery negative electrode active material liquid was subjected to CV measurement under the following conditions, the CV diagram shown in FIG. 2 (shown as addition of hydrochloric acid in the figure) was obtained. In the obtained CV diagram, a large oxidation wave of divalent vanadium was detected.

Conditions and working electrode for CV measurement: Graphite electrode (0.5 mmφ × 10 mm ^h (liquid depth), X-ray 002 diffraction peak half-value width 2.6 °)
・ Reference electrode: Ag / AgCl
-Potential sweep speed: 50 seconds / V
・ Temperature: 22 ℃
・ State: Stationary electrode, Stationary active material liquid

(Comparative Example 1)
A battery negative electrode active material solution was obtained in the same manner as in Example 1 except that the addition of hydrochloric acid in Example 1 was omitted. The viscosity of this liquid was 6 cp.

<CV measurement>
When the obtained battery negative electrode active material solution was subjected to CV measurement under the same conditions as in Example 1, the CV diagram shown in FIG. 2 (shown as no addition of hydrochloric acid in the figure) was obtained. In the obtained CV diagram, a slight oxidation wave of divalent vanadium was detected. It can be seen that the oxidation current of this oxidation wave is significantly smaller than the CV diagram of Example 1.

2. Battery positive electrode active material liquid (Example 2)
By electrolytic reduction of a solution containing 3.5 M VOSO ₄ and 2.0 M H ₂ SO ₄ in water, the molar ratio of trivalent vanadium and tetravalent vanadium was 1: 1 (3.5 valence). Furthermore, this solution was electrolytically oxidized to obtain a solution containing tetravalent and pentavalent vanadium. The viscosity of this liquid was 11 cp.

Subsequently, hydrochloric acid was added to the obtained liquid so as to satisfy the above-described condition of the chemical shift value of the ¹ H-NMR spectrum. As a result, the hydrochloric acid concentration in the liquid became about 1M. This was used as a battery positive electrode active material liquid. The viscosity of the solution after addition of hydrochloric acid was 6 cp.

^<1 H-NMR spectrum measurement>
The obtained battery positive electrode active material solution was subjected to ¹ H-NMR spectrum measured at a resonance frequency 200kHz, ¹ H-NMR spectrum shown in was obtained Fig 1 (c). The chemical shift value δ _a (21 ppm) of the resonance absorption peak of the battery positive electrode active material liquid corresponds to 1.75 times the chemical shift value δ _b (12 ppm) of the resonance absorption peak of the sulfuric acid aqueous solution. The condition (1.2 times or more) is satisfied.

<CV measurement>
When the obtained battery positive electrode active material liquid was subjected to CV measurement under the following conditions, the CV diagram shown in FIG. 3 (shown as addition of hydrochloric acid in the figure) was obtained. In the obtained CV diagram, a large reduction wave of pentavalent vanadium was detected.

Conditions and working electrode for CV measurement: Graphite electrode (0.5 mmφ × 10 mm ^h (liquid depth), X-ray 002 diffraction peak half-value width 2.6 °)
・ Reference electrode: Ag / AgCl
-Potential sweep speed: 50 seconds / V
・ Temperature: 22 ℃
・ State: Stationary electrode, Stationary active material liquid

(Comparative Example 2)
A battery positive electrode active material solution was obtained in the same manner as in Example 2 except that the addition of hydrochloric acid in Example 2 was omitted. The viscosity of this liquid was 11 cp.

<CV measurement>
When the obtained battery positive electrode active material solution was subjected to CV measurement under the same conditions as in Example 2, the CV diagram shown in FIG. 3 (shown as no addition of hydrochloric acid in the figure) was obtained. In the obtained CV diagram, a slight reduction wave of pentavalent vanadium was detected. It can be seen that the reduction current of this reduction wave is significantly smaller than the CV diagram of Example 2.

3. Low temperature characteristics of active material liquid (Example 3)
The molar ratio of trivalent vanadium and tetravalent vanadium was set to 1: 1 by electrolytic reduction of a solution containing 2.6 M VOSO ₄ and 5.0 M H ₂ SO ₄ in water. The viscosity of this liquid was 10 cp.
Furthermore, this liquid was subjected to electrolytic reduction to obtain a liquid (negative electrode active material liquid) containing divalent and trivalent vanadium. The viscosity of this negative electrode active material liquid remained at 10 cp.

Next, when hydrochloric acid was added to the obtained liquid so as to satisfy the chemical shift value of the ¹ H-NMR spectrum described above, the viscosity decreased to 6 cp. As a result, the hydrochloric acid concentration in the liquid became 1M.

<CV measurement>
About the obtained battery negative electrode active material liquid, when CV measurement was performed on the following conditions in each temperature of 25 degreeC and 0 degreeC, the CV figure shown in FIG. 4 was obtained. From the obtained CV diagram, the oxidation current of divalent vanadium at 25 ° C. was 550 μA, and the oxidation current of divalent vanadium at 0 ° C. was 320 μA.
Moreover, the magnitude of the peak area ratio at 0 ° C. and 25 ° C. on the CV diagram is considered to indicate the reactivity (electrode reaction rate), and also from the ratio of the peak sizes at 0 ° C. and 25 ° C. It can be seen that the active material liquid of the present invention has a good anti-reflection.

Conditions and working electrode for CV measurement: Graphite electrode (0.5 mmφ × 10 mm ^h (liquid depth), X-ray 002 diffraction peak half-value width 2.6 °)
・ Reference electrode: Ag / AgCl
-Potential sweep speed: 50 seconds / V
・ Temperature: 25 ℃ and 0 ℃
・ State: Stationary electrode, Stationary active material liquid

(Comparative Example 3)
Let's obtain a battery negative electrode active material liquid containing divalent and trivalent vanadium by electrolytic reduction of a liquid containing 3.0 M VOSO ₄ and 5.0 M H ₂ SO ₄ in water without adding hydrochloric acid. However, crystals considered to be divalent vanadium salts were precipitated.

<CV measurement>
About the obtained battery negative electrode active material liquid, when CV measurement was performed on the following conditions in each temperature of 25 degreeC and 0 degreeC, the CV figure shown in FIG. 5 was obtained. From the obtained CV diagram, the oxidation current of divalent vanadium at 25 ° C. was 380 μA, and the oxidation current of divalent vanadium at 0 ° C. was 115 μA.
Moreover, the magnitude | size of each peak area ratio in 0 degreeC and 25 degreeC on a CV figure expanded greatly in the system which has not added hydrochloric acid.

Conditions and working electrode for CV measurement: Graphite electrode (0.5 mmφ × 10 mm ^h (liquid depth), X-ray 002 diffraction peak half-value width 2.6 °)
・ Reference electrode: Ag / AgCl
-Potential sweep speed: 50 seconds / V
・ Temperature: 25 ℃ and 0 ℃
・ State: Stationary electrode, Stationary active material liquid

<Evaluation of low-temperature characteristics of active material liquid>
As described above, in Example 3 using the battery negative electrode active material solution to which hydrochloric acid was added, the oxidation current of divalent vanadium at 25 ° C. was 550 μA, and the oxidation current of divalent vanadium at 0 ° C. was 320 μA. At this time, the ratio of the oxidation current of the battery negative electrode active material liquid at 0 ° C. to the oxidation current of the battery negative electrode active material liquid at 25 ° C. (that is, the estimated output value of the 0 ° C. electrolyte to the 25 ° C. electrolyte) is 58%. (Table 1).

  On the other hand, in Comparative Example 3 using the battery negative electrode active material liquid to which hydrochloric acid was not added, the oxidation current of divalent vanadium at 25 ° C. was 380 μA, and the oxidation current of divalent vanadium at 0 ° C. was 115 μA. At this time, the ratio of the oxidation current of the battery negative electrode active material liquid at 0 ° C. to the oxidation current of the battery negative electrode active material liquid at 25 ° C. (that is, the estimated output value of the 0 ° C. electrolyte to the 25 ° C. electrolyte) is 30%. (Table 1).

  Further, the respective peak areas at 0 ° C. and 25 ° C. show the effect of addition of hydrochloric acid similarly to the peak height. From this, it can be seen that, compared with Comparative Example 3, Example 3 can prevent the deposition of vanadium and maintain the battery output even when the temperature is lowered.

  From the above results, it can be seen that the battery negative electrode active material liquid added with hydrochloric acid is excellent in low temperature characteristics. Thereby, the effect which can maintain a battery output stably with respect to a temperature change is show | played. In addition, although the example of the battery negative electrode active material liquid was given here, the same result was obtained also in the case of the battery positive electrode active material liquid.

Claims (6)

A negative electrode active material liquid or a positive electrode active material liquid of a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more,
By adding chloride, the chemical shift value of the proton peak in the proton nuclear magnetic resonance spectrum is 1.2 to 5 times the chemical shift value in a 0.1 M to 10 M sulfuric acid aqueous solution. Active material liquid. A positive electrode active material solution for a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more,
The chemical shift value of the proton peak in the proton nuclear magnetic resonance spectrum is 1.2 to 5 times the chemical shift value in a 0.1 M to 10 M sulfuric acid aqueous solution,
An active material liquid, wherein 0.2 M or more of chloride ions coexist with vanadium. A negative electrode active material solution for a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more,
By adding chloride, the reaction electricity quantity of the oxidation wave of divalent vanadium in the current-potential curve observed by the potential sweep method is the reaction quantity Q ₀ measured at 0 ° C., and at 25 ° C. An active material liquid, wherein a ratio (Q ₀ / Q ₂₅ ) of measured reaction electricity Q ₂₅ is 0.3 to 1.0. A positive electrode active material solution for a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more,
By adding chloride, the reaction electric quantity Q ₀ measured at 0 ° C. as the reaction electric quantity of the pentavalent vanadium reduction wave in the current-potential curve observed by the potential sweep method, and at 25 ° C. An active material liquid, wherein a ratio (Q ₀ / Q ₂₅ ) of measured reaction electricity Q ₂₅ is 0.3 to 1.0.   Viscosity is 6 cp or less, The active material liquid in any one of Claims 1-4 characterized by the above-mentioned. When manufacturing a negative electrode active material liquid or a positive electrode active material liquid of a vanadium redox secondary battery that is acidic with sulfuric acid and has a total vanadium concentration of 2.5 M or more,
After electrolytic reduction of the vanadyl sulfate solution to make the molar ratio of trivalent vanadium and tetravalent vanadium 1: 1,
The chemical shift value of the proton peak in the proton nuclear magnetic resonance spectrum measured for the liquid in at least one of the following states (I) to (III) is 1.2, which is the chemical shift value in a 0.1 M to 10 M sulfuric acid aqueous solution. A method for producing an active material solution, wherein the sulfuric acid concentration and the chloride concentration are adjusted so as to be ˜5 times.
(I) Liquid in which the molar ratio of trivalent vanadium and tetravalent vanadium is 1: 1 (II) Liquid containing divalent vanadium and trivalent vanadium obtained by electrolytic reduction of the liquid described in (I) A liquid containing tetravalent vanadium and pentavalent vanadium obtained by electrolytic oxidation of the liquid described in (I).

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